Double consonants are two of the same letters together, such as in the word 'letter' (t is seen twice). Consonants are letters of the alphabet that are not vowels (a, e, i, o, u). As always in English, it's not so straightforward.

Let's take the word cut. When we add er, do we need to add an extra t or not? In this case we do. Cut, cutter, cutting. If we left it with just one t, it would be cuter which means more cute.